X-ray absorption spectroscopy (XAS) is a valuable technique for studying a variety of metal sites in biological systems. The technique measures the transition of core electronic states of the metal to excited electronic states or continuum states. Spectral analysis near the electronic transition (x-ray absorption near-edge structure or XANES) provides information on the metal's charge state and geometry. Spectral analysis above the absorption edge (from the edge to 10-15 percent above the edge in energy), so called Extended X-ray Absorption Fine Structure or EXAFS, provides complementary structural information like, numbers, types, and distances of ligands or neighboring atoms. The Albert Einstein Center for Synchrotron Biosciences, an NIH Resource Center at the National Synchrotron Light Source, operates a beamline (X9B) and provides comprehensive user support that has provided access to x-ray spectroscopy experiments for NIH funded investigators for over 10 years. This proposal requests an Advanced Array Detector for X-ray spectroscopy that can count 3 times faster than our existing detector. Recent improvements in beamline X9B make current XAS experiments inefficient. The 4 fold increased x-ray flux now available for XAS experiments cannot be adequately handled by the antiquated electronics of the existing XAS detector. XAS is a major component of the NIH funded programs of each of the 7 major users listed in the proposal. These users have 13 NIH grants that will benefit from this instrument. These users also have over 60 XAS publications in the last three years using the facilities and current detector of the Resource Center. In addition, these major users identify 18 NIH funded collaborators (with 20 additional NIH grant programs pertinent to the proposal) who will benefit from the acquisition of this instrument. The available beamtime for XAS on the X9B beamline is 2-fold oversubscribed. These NIH funded users and their collaborators have few alternatives for completing their experimental programs. Increasing throughput by a factor of three using the new instrument would be an extraordinary benefit to this productive and well-funded user community.